1. FIELD OF THE INVENTION
This invention relates generally to apparatus for conveying particulate material such as gunite, refractories, or the like to and through a delivery tube; and more particularly to such an apparatus that has an improved sealing system.
2. PRIOR ART
For purposes of this document, particulate material includes material in the range of sizes extending from dusts through gravel; and the term "conveying" encompasses projecting as from a gun.
Most commercially available apparatus for conveying particulates generally follows one of two basic configurations. U.S. Pat. No. 3,161,442, issued to Frank A. Reed in 1964, introduced one of those configurations and is hereby incorporated by reference in its entirety.
For convenience the drawings of Reed's patent are adapted here as FIGS. 4 through 10, described later in this document.
Reed shows apparatus 10R that includes a hopper 11R with top and bottom circular openings 12R, 13R containing stationary and rotary agitator blades 14R, 15R--the latter mounted on a rotary shaft 16R. The shaft, held in a bearing 17R in a base 18R, is driven through a gear train 19R by a fluid motor 20R.
A valve 21R receives fluid from a supply 22R via a regulator 23R, to control the motor. Exhaust air is muffled at 24R. Keyed to the shaft is a feed rotor 30R, whose face 31R receives material at the lower opening 13R.
A housing 32R shrouds some 45.degree. of the lower opening, above an expulsion station 33R, leaving the face 31R open to the hopper over about 315.degree.. Formed in the rotor 30R about its central axis 38R are two concentric sets of ports 34R, 35R, each radially associated pair of ports forming an upright U-shaped pocket 39R with a round bottom 40R, baffle 41R and radial walls 42R.
An orifice plate 43R is fixed in the housing 32R by screws 44R through a hose baseplate 44aR. The plate 43R has inlet and outlet conduits 45R, 46R--and holds inlet and outlet hoses 48R, 49R--for alignment with the ports 34R, 35R respectively.
A rubber pad 47R (FIGS. 7 and 9) on the orifice plate 43R is pressed against the rotor face 31R screws 44R, and rubs against the face when the rotor 30R turns. Unregulated fluid from the supply 22R is applied to the inlet hose and port 48R, 46R to blow granular material through the pockets 39R--as they rotate into registration with the ports 45R, 46R--and out through the outlet port and hose 46R, 49R to a place of use.
Another basic configuration, generally used by European manufacturers, may be exemplified by U.S. Pat. No. 4,462,719 for a "Concrete Gun", which issued Jul. 31, 1984, to Hans R. Egger and Rudolf Vogler, based upon a 1981 Swiss application.
Such machines are usually mounted on a wheeled cart; and all include means defining a receiving port for receiving such material from a hopper. In both of the basic configurations the receiving port is essentially the bottom of the hopper, but in the European configuration it also includes an annular arcuate opening in a disc-shaped structure just below the hopper--as will be described shortly.
Such apparatus also includes means defining a discharge port for discharge of such material into a delivery tube. In Reed's system the discharge port is immediately adjacent to the receiving port, whereas in the European system they are separated by another element which we shall take up next.
At the heart of both systems is a feed structure mounted for rotation and defining many parallel chambers (in principle at least one such chamber is required) for receiving material from the receiving port, and for carrying received material by that rotation to the discharge port for discharge. This structure is generally of steel, and in the Reed configuration is usually called a "feed rotor".
Both the Reed configuration and the European configuration also include pneumatic means, defining and including a pneumatic supply orifice, for applying gas to blow material from the feed structure into the discharge port. The same pneumatic blast also propels the material through the discharge port into the delivery tube, and typically projects the material from the remote end of that tube to a delivery point at a construction site or the like.
Reed's preferred design calls for each chamber to take the shape of a "U"-shaped tube, often called a "pocket"--with a central partition extending partway to the bottom. In this arrangement accordingly the receiving and discharge ports are both at the same side of the feed structure.
This is the reason for the immediate adjacency, mentioned earlier, of those two ports. The "U" shapes of all the individual pockets, when formed in a circular array about the axis of the feed rotor, gives the feed rotor a distinctive bowl-shaped appearance; the feed rotor is therefore sometimes called a "feed bowl" or familiarly just a "bowl".
The axis of rotation is vertical, and the "U" shapes are all erect and right-side-up, so that each pocket in the bowl is open at the top as is an ordinary bowl. Typically the bowl has a floor that is generally continuous and solid, though rounded. The floor forms the adjacent bottoms of all the pockets in common, and typically is perforated only by an axle-mounting hole at its center.
In the machines of European configuration, by contrast, the chambers are all straight and pass completely through the feed structure, so that it somewhat more closely resembles a rotary bullet-shell magazine in a hand revolver--but, here too, with the axis of rotation vertical. The receiving and discharge ports in such a configuration thus are at the two opposite ends (namely, the top and bottom respectively) of the feed structure.
The pneumatic supply orifice is also at the top of the structure. It is aligned above the discharge port at a generally common angular position about the axis, so that air from that orifice can blow material into the discharge port.
Both configurations include sealing means for substantially sealing a pneumatic path defined by the pneumatic supply orifice, the discharge port, the delivery tube, and at least one chamber when generally in position for discharge. It can now be appreciated, however, that in the Reed system a single unitary seal (usually called a "pad") suffices for the complete sealing function--since the pneumatic path passes in and out of the feed bowl at exclusively one side (namely, the top) of the bowl.
In the straight-through configuration, however, two separate seals are required. One seal (sometimes called a "joint plate" or "sealing plate") is at the top, to seal the inlet half of the pneumatic path: the junction between the pneumatic supply orifice and the chamber. The other seal (sometimes known as the "gasket plate" or "sealing plate") is at the bottom, to seal the outlet half of the path: the junction between the chamber and the discharge port and delivery tube.
Our phrase "sealing means" encompasses both a single unitary seal as in the Reed system, and two discrete seals as in the European systems. It also encompasses other seal configurations, whether unitary or plural. In all gunite and refractory guns, as far as we are aware, the sealing means are of hard rubber or the like; however, other elastomers or elastomer-like materials possibly could be used.
There is another difference between the sealing means used in the two configurations. In the European machines, both the top and bottom seals cover almost the entire circular surfaces at top and bottom respectively.
At the bottom, almost the only significant aperture in the seal is at the discharge port--and that is only of a relatively small areal extent, generally equal to the area of one or two chambers. This small aperture thus exposes the bottom of the particular chamber or chambers that are rotated into position for discharge.
The bottom seal, generally circular, must cover all the rest of the chambers at their bottom ends. In these machines the bottom seal not only stands off the air pressure, but also supports the material against gravity. The generally circular seal forms the floor of every chamber and is thus the only thing holding the material in the chambers as they rotate.
Similarly the seal at the top of the feed rotor has a small aperture at the pneumatic supply orifice--aligned directly above the discharge port. In addition, however, the top seal has a much larger aperture, for admission of material from the hopper.
This aperture, which may be regarded as part of the receiving port, usually is annular and spans an arc of perhaps eighty to one hundred degrees. The seal is generally a circular disc, and its center and periphery--that is, the portions radially inward and outward from the annular aperture--are substantially continuous all the way around the circle.
In Reed's configuration, by contrast, the seal covers only a relatively narrow sector of the circular top surface of the feed structure. In principle it could be extended around the rest of the circular surface, except for the annular region through which particulate material falls into the open tops of the chambers, as in the European machines. For historical reasons, however, the seals have never been so formed in machines of the Reed configuration. Conversely in principle the top seals of the European systems could be restricted to only a narrow sector.
Both configurations also include mechanical means for applying force to press the sealing means against the feed structure. As will be seen, these means are of particular importance to the present invention; we shall shortly discuss them in detail.
Such a pressed-together seal must be maintained while the feed structure rotates. Of course this entails a sliding and rubbing contact between the sealing means and the feed structure.
As will be understood the resulting abrasion by the material being conveyed can very severely erode the rubber sealing means or the steel feed structure, or most typically both. Such erosion in fact has been found particularly troublesome in both of the configurations discussed above, leading equipment manufacturers to try a variety of divergent approaches to controlling it.
In the commercial implementation of the Reed configuration, bowl damage from this erosion has led to fabrication of some bowls in two sections. A bottom section defines the "U" shapes of the bottoms of all the pockets; and an upper section, usually only about an inch tall, has the same pattern of walls and apertures as the bottom section and is carefully aligned over the bottom section.
This thin upper section is separately fabricated merely to facilitate its replacement without the need for replacing the entire bowl. This extension of the bowl accordingly is termed a "wear ring" or "wear plate", while the nomenclature "the bowl" is sometimes reassigned to refer to the bottom section, even though in a sense that element is only part of the two-piece bowl.
Some machines of the European configuration are similarly split--but into three sections rather than only two, because of the separate seals. Thus wear rings or plates (sometimes in these machines also called "rotor plates") appear at both top and bottom. The term "feed rotor" is then reassigned to the remaining center section.
In any event our phrase "feed structure" used in this document for machines of the bowl configuration encompasses both parts, however they may be designated--that is, both the "wear ring" and "the bowl", or "both sections of the bowl", etc. For machines of the European straight-through configuration, our phrase "feed structure" analogously encompasses all three parts, however designated--the two "wear plates" and "the rotor", or "all three sections of the rotor", and so forth.
Each rubber seal is usually vulcanized to a respective steel or cast-iron mounting plate, which is later discarded with the seal (or recycled to a new seal) when the seal is worn out. Pressing against each of these mounting plates is a heavier metal part that is a permanent piece of the machine and that is sometimes called a "pad backup plate" or the "pad housing" in the Reed configuration, and a "clamp plate" in the European units.
For purposes of this document both the vulcanized-on plates and the pad backup, housing or clamp plates may be regarded as part of the mechanical means for applying force to press the sealing means against the feed structure. The pad backup, housing or clamp plates, however, also serve as mountings for a tube from the pneumatic supply system, and for a delivery-tube attachment fitting (in the Reed units, a short strong metal pipe called the "gooseneck").
Therefore the various plates just discussed may also (or instead, if preferred) be considered parts of the pneumatic means, the discharge port, and the delivery tube. As the four elements--the mechanical means, pneumatic means, discharge port and delivery tube--effectively come together at these points, the backup, housing or clamp plates usually serve as parts of all four.
The mechanical force-applying means, in addition to these plates, have taken a great variety of forms. One such form, for a Reed-style machine, consists of an elaboration of the adjusting screws 44 shown in FIG. 7 of the Reed patent.
In that elaborated clamping mechanism, three spaced-apart parallel adjusting studs are controlled by a system of three knobs, two sprockets, and three chains--the sprockets and chains operating in grease within a sealed housing. The studs are threaded vertically through the pad housing or backup plate, and bear directly (just below that housing or plate) against the mounting plate to which the pad is vulcanized.
Each handle, through its associated sprockets and chain, operates the top end of one of the studs, respectively. In this way force is manually applied at the corresponding three spaced-apart points to press the pad against the bowl or wear plate. Because force is applied rather directly, a careful operator may be able to obtain a good "feel" for the amount of force being applied.
Another form, also in a machine of the configuration patented by Frank Reed, consists of two cams, spaced apart near opposite edges of the pad, and operating about parallel horizontal axes to bear against the pad-backup plate or housing. Each of the two cams is secured to a respective horizontal pin, several inches long, for rotation with the pin.
Each cam also is split into two cam sections--one near each end of the pin. The pin is actuated near its center by a lever, which in turn is manually operated (as for example through a system of leadscrews and handles). This two-stage system, as will be appreciated, may possibly provide greater mechanical advantage and thus in theory a greater degree of control over the force applied to the pad--though perhaps somewhat less sensitivity to the level of force that is being applied.
Another way of pressing the seal or seals against the feed structure has been used in some European machines. That approach uses a hydraulic system, with a plurality of actuators.
The stems of these actuators, bearing against the clamp plates, constitute yet a third form of mechanical means for applying force to press the sealing means against the feed structure. In this arrangement a manually operated hydraulic jack is used to control the hydraulic system.
The jack is set at a desired position. Here too, as will be understood from the known properties of hydraulic systems, such apparatus provides quite delicate control of the force applied to the gasket plates or joint plates, etc.
Other systems that have been employed are generally variations of these three. Unfortunately, despite the variety of seemingly reasonable means employed for this purpose, it is well known in the industry--and has been well known for more than twenty years!--that seals and feed structures in all these machines are subject to severe and irregular wear.
Such wear is a significant problem to operators and owners of these machines. First, although the seals themselves represent a relatively small fraction of the total cost of a machine, the machines have useful lives of many years; thus the cost of seal replacement usually represents a relatively large fraction of the annual amortization and operating cost. The same is even more emphatically true of feed-structure (or even wear-ring) replacement.
Perhaps more importantly, the inconvenience and great costliness of machine down time for seal replacement are very significant. This is particularly so when wear is irregular or erratic and therefore unpredictable, and excruciatingly so in relatively remote work sites where replacement seals may not be readily available.
It is not unusual for a contractor working in a small city or remote rural job site to be forced to stop work for hours or even days while a source of replacement seals is sought frantically. It is rather commonplace for replacement seals to be carried by air courier to an inoperable machine.
Guns of Reed's configuration have proven to be relatively advantageous in terms of seal replacement. The seal is relatively small and hence inexpensive, and is mounted only at one edge of the feed structure--and only on its top.
Thus the seal is very quickly and easily removed through a small access port at the side of the machine, just below the hopper. Despite these advantages, the problems of seal and wear ring erosion as already described are notorious even with Reed-type machines.
From the character of the European configuration it will be clear that far more extensive disassembly and reassembly are required for seal replacement, particularly with respect to the bottom seal or gasket plate. Many operators have a fully understandable, if unfortunate, aversion to performing such operations under field conditions. In some cases such an aversion may aggravate the eventual outcome by delaying needed work until it becomes unavoidable at times or places that are particularly inconvenient.
In the European machines, from what was said earlier about seal geometry, the seals also are far larger, elaborate in construction, and expensive than those for the Reed configuration. Hence they are not found in stock as readily in outlying areas.
Perhaps the European seal configuration may be somewhat less sensitive to incorrect or unbalanced clamping force, as clamping force and therefore wear are distributed over a greater area--namely, the entire surface--at both top and bottom, so that replacement may be required less frequently. On the other hand, wear at the bottom seal is somewhat aggravated by the fact that material is pressed against that seal by gravity--acting on the full load of material in the hopper, pressing down upon the material in each chamber.
Furthermore, the fact that seal replacement in the European machines is less frequent but difficult has its own drawbacks, particularly when the replacement schedule is unpredictable because the wear is irregular or erratic. These conditions in combination simply mean that the experience and skill (as well as the seals) needed for a quick and correct replacement operation are less likely to be available when the time comes.
In any event, seal-replacement problems in machines of the Reed configuration, as already noted, are significant and notorious. In machines of the European configuration these problems can readily become catastrophic--although possibly at a lower frequency.
Hence for both types of equipment there is and for many years has been a major unmet need for improvement in the control of seal wear. Our invention is directed to this need.